1. Field of the Invention
The present invention relates to the monitoring of mobile and remote endpoint devices over a very large area of service.
2. Discussion of the Background
Asset management is a critical part of any business entity engaged in the transfer of raw or finished goods. It is important to carefully manage resupply of raw materials to ensure that the manufacturing or service element of an industry does not halt and to carefully manage transportation of finished goods to minimize inventory held for sale. Those companies that do not optimize manufacturing and materials handling are at a significant disadvantage.
The uncertainty associated with raw materials and finished goods in transit presents a problem in asset management. Companies generally operate with an element of uncertainty as to the exact time of delivery or location of pending delivery for products and raw materials in transit. Unforeseen conditions impacting the arrival of truck, rail, or other vessel deliveries are impossible to predict and difficult to model. Real-time information about material in transit can be used to forecast deliveries, schedule manpower and other materials, and predict finished goods inventory supply.
The transportation industry estimates in excess of 40 billion dollars a year in cargo theft lost in transit. Loss of cargo happens in a wide variety of ways, from employee/driver theft to the organized capture of entire fleets of trailers and rail-cars. The transportation industry has been struggling to limit loss through radio communication means for over a decade. The cellular telephone industry has enabled a host of communications products that are making an impact. These products provide many functions from standard voice communication data services such as Internet or E-mail, and real-time position reporting and status of vehicle operations such as speed, temperature, or brake conditions.
Conventional solutions typically rely on cellular communication systems or satellite communication systems. Existing technology solutions that rely on cellular coverage are generally not ubiquitous in coverage. Cellular coverage may be adequate for urban and major interstate routes but becomes unreliable in rural or sparsely populated regions. Additionally, a cellular network implemented primarily for voice commerce is a poor solution for rail or vessel transportation data communication. Also, as cellular technology advances, the protocols have transitioned from analog to digital and now to tri-band Global System for Mobile Communication (GSM). Thus, some communications systems developed only a few years ago are already obsolete.
Additionally, cellular communication asset management systems are inherently two-way in nature and thus require continuous line power for operation. This type of system does not operate effectively on battery power only without periodic reconnection to line power such as the automotive power system.
Satellite based communication systems mitigate some of the problems associated with cellular asset management devices. For instance, satellite modems are not limited to the service coverage area of cellular telephone corridors. Instead, the area of service is related to the satellite system selected for use and thereby solves the problem of rural and vessel coverage.
Satellite asset management systems are preferred if the communication system can provide adequate information bandwidth to support the application requirements. Generally, satellite asset management systems are the successors of cellular systems and offer broadband feature sets such as Internet and voice over Internet-Protocol. Broadband satellite services are typically expensive and generally prone to communication failures due to weather and obstruction. Most asset management systems which utilize broadband satellite must package broadband services such as voice, or Internet in order to justify the cost of the data bandwidth even though the information for asset management is generally low-bandwidth in nature. This drives the cost of satellite-based asset management systems up in order to package enough value to offset cost.
Additionally, the transmit power required to communicate to geo-stationary satellites imposes power system problems for a remote asset management device. Existing satellite asset management systems generally must incorporate transmit power amplifiers of up to 10 Watts to adequately operate. As most satellite communication systems impose tightly controlled spectral masks, digital communication systems must incorporate linear or nearly linear (Class A or Class AB) power amplifier architectures to prevent spectral regrowth. As a result, the transmit device must be designed to produce up to 10 Watts with amplifier architectures which are typically only 40% efficient. This creates difficult design limitations which predominately require sufficient line power or high-density bulky battery systems to function.
Currently, satellite-based asset management systems use satellite architectures that are duplex in nature. In order to send data over a satellite, the remote device must generally negotiate a data channel. Even if the data is only one-way in nature, the communication modem must contain both receive and transmit capability to implement this negotiation. Remote asset management devices must both listen and transmit in order to facilitate data transfer to and from a remote device.
Both cellular and two-way satellite asset management systems require available line power or extensive battery systems to operate. Even existing systems equipped with low power operational states must utilize excessive power to manage two-way communications as well as transmit with sufficient energy to operate within the communications infrastructure.
Existing asset management devices are generally located on the tractor-cab of the truck, train or vessel. This serves to locate the cargo while the load is attached. Unfortunately, when a load such as the trailer, rail-car, or barge is disconnected, the important information that provides value for asset management is lost. Trailers that get dropped-off by a driver may become lost for hours or days possibly resulting in the total loss of perishable loads, or missing deadlines for non-perishable loads that are often time critical. Thus, inventory management becomes difficult and highly labor intensive to minimize misplaced loads.
Rail-car tracking systems generally lag in capability behind trucking. While rail-cars remain on class 1 lines, the owners typically know when the rail-cars have passed checkpoints using barcode or visual identification systems, but once the rail-cars are placed on class 2 or class 3 lines there is generally no real-time tracking. Additionally, customers often use rail-cars as temporary storage thereby delaying offloading goods to maintain an average amount of storage of goods at the cost of the rail-fleet owner. Rail-fleet owners have a difficult time assessing demurrage charges because they may not know if the rail-car has been offloaded on schedule or where the rail-car is currently located. As a result, the only solution generally applied is to add new cars to the fleet to satisfy logistic problems of moving goods.
Barge and vessel owners generally are dependent on river pilots and deep-sea vessel operators for the location of goods using voice communication only. As such, commodity traders usually maintain a staff of logistics personnel to voice-track products as they are moved. A radio-telemetry product that works without a cellular infrastructure and without the requirement of available power can thus dramatically reduce the reliance of pilots and logistics staff.
By way of further background regarding methods of transmitting data, FIG. 2 of U.S. Pat. No. 4,977,577, previously incorporated by reference, shows a transmitter including chip-code-generation means, preamble means, address means, data means, timing means, pseudorandom-sequence means, and error-detection means. The chip-code-generation means may be embodied as a recirculating register 10 and the preamble means may be embodied as a preamble register 11. The chip-code-generation means may be embodied as a shift register with exclusive ORed feedback taps. The address means may be embodied as an address register 14, the data means may be embodied as a data register 18, and the error-detection means may be embodied as cyclical-redundancy-check (CRC) generator 19. The timing means may be embodied as timing circuit 13, and the pseudorandom sequence means may be embodied as the random number generator 17.
In the exemplary arrangement shown, a microprocessor 8 includes the recirculating register 10, preamble register 11, address register 14, data register 18, CRC generator 19, random number generator 17, and timing circuit 13. The timing circuit 13 is embodied as a timing algorithm in software, located in microprocessor 8. Alternatively, these registers and circuits may be put together with discrete components or independently wired and constructed as separate elements, as is well known in the art.
As shown in FIG. 8, an oscillator, which is shown as a voltage controlled oscillator 2 is coupled to an RF power amplifier 3, and the RF power amplifier 3 is coupled through a bandpass filter 4 to a micropatch or equivalent antenna 5. The voltage controlled oscillator 2 includes an enable input and a modulation input, where the voltage controlled oscillator generates a spread spectrum signal in response to a modulating voltage being applied to the modulation input. The voltage controlled oscillator 2 is enabled by applying an enable signal to the enable input. The RF power amplifier 3 has a keying input and will amplify a signal from the voltage controlled oscillator 2 only if a keying signal is applied to the keying input. The voltage controlled oscillator 2 alternatively can be frequency locked to the microprocessor's crystal to improve stability. The voltage controlled oscillator 2 also can be replaced by a capacitor and inductor tuned oscillator and a phase shift keyed modulator, or any other means for generating a signal.
The microprocessor 8 is coupled to the modulation input of the voltage controlled oscillator 2 through first resistor R6 and second resistor R7. The microprocessor 8 broadly controls the voltage controlled oscillator 2 by supplying an enable signal to the enable input of the voltage controlled oscillator 2, and a modulating voltage to the modulation input of the voltage controlled oscillator 2. Also, the microprocessor 8 controls the RF power amplifier 3 by supplying a keying signal to the keying input of the RF power amplifier 3.
Included in the microprocessor 8 is a recirculating register 10 coupled to the modulation input of the voltage controlled oscillator 2 through second resistor R7. The recirculating register 10 stores a spread spectrum chip code, and outputs, during a transmitting interval, the spread spectrum chip code as a modulating voltage to the modulation input of voltage controlled oscillator 2.
The preamble register 11 is coupled to the modulation input of the voltage controlled oscillator 2 through first resistor R6. The preamble includes the coarse lock preamble and the fine lock preamble. The preamble register 11 stores a coarse lock preamble in cells 12 and a fine lock preamble in cells 24. The preamble register 11 outputs during the transmitting interval, the coarse lock preamble and the fine lock preamble as a modulating voltage to the modulation input of the voltage controlled oscillator 2 through first resistor R6. First resistor R6 and second resistor R7 are chosen such that the desired spreading from the chip code and the data coming from the preamble register 11 is achieved.
Also shown in FIG. 8 is an address register 14 coupled to the modulation input of the voltage controlled oscillator 2 through the preamble register 11 and first resistor R6. The address register 14 stores a device address and a type code, and outputs during a transmitting interval, the device address and type code as a modulating voltage to the modulation input of the voltage controlled oscillator 2.
A data register 18 is coupled to a data input 20 and to the modulation input of the voltage controlled oscillator 2 through the preamble register 14 and the address register 11. The data register 18 stores data received from the data input, and outputs, during the transmitting interval, the data as a modulating voltage to the modulation input of the voltage controlled oscillator 2. The data from the preamble register 11, address register 14, and data register 18 are outputted in sequence, and at the end of a sequence, the cyclical redundancy check generator 19 outputs a data word at the end of the code for error detection.
A timing circuit 13 is included in microprocessor 8, and is coupled to the enable input of the voltage controlled oscillator 2 and to the keying input of the RF power amplifier 3 for enabling the voltage controlled oscillator 2 and the RF power amplifier 3, by outputting an enable signal to the enable input and a keying signal to the keying input of the RF power amplifier 3, respectively, during the transmitting interval. In essence, voltage controlled oscillator 2 and RF power amplifier 3 are not active or activated during a time duration of non-transmission, and are only activate during a transmission interval. The time duration between transmission intervals is made to vary in response to the random number generator 17 generating a random number and transferring the random number to the timing circuit 13. The random number modifies the timing duration between each transmitting interval randomly.
Also shown are the voltage supply, regulator circuit 1, and battery low detector 25.
The spread spectrum transmitter monitors one or more data inputs 20 and transmits periodically a supervisory data message. One or more of the data inputs 20 can be set 21 such that they cause a priority transmission at an increased rate higher than the supervisory message rate.
During installation of the transmitter, a device address (1-4095) 12, “Type” code 15 (fire, security, panic, heat, pull station, etc.) stored in preamble register 11, and a spread spectrum chip code stored in recirculating register 10 are loaded via programming connector 16. At installation time the “Panel” computer assigns the device ID address to each room number or unique device in the system which is to be monitored. The panel computer then prints a sticky label with the device's ID, address, type code and spread spectrum chip code, both in decimal and bar code form. The label is fixed to the smoke detector or alarming device and via the programming connector 16, or the number can be entered manually with the aid of a hand-held terminal. Alternatively a bar code reader can be connected to the programming connector 16 and the device can be read electronically from the bar code and entered into the transmitter. Microprocessor timing is controlled by crystal 23. Transmit timing is controlled by the wake-up timer 9, which has its own low power oscillator.
In operation, the transmitter sends a supervisory message often enough so that the receiver can detect failure of any transmitter within 200 seconds. The microprocessor 8 effectively “sleeps” between these transmissions to conserve battery life while counter 9 counts down to wake-up microprocessor 8. In order to minimize the chance of reoccurring data collisions from multiple simultaneous transmitters, the transmit interval is modified by random number generator 17. Very fine resolution intervals are used equal to 500 temporal transmit positions. The random number generator 17 is seeded with the transmitter's unique address 14, resulting in different transmit schedules for each unit, thereby avoiding continuous collisions between transmitters.
Once the microprocessor 8 is reset by the wake-up circuit 9 the timing circuit 13 allows the crystal 23 to stabilize for 1–5 ms. The timing circuit 13 then enables the transmitter oscillator 2 and allows it to stabilize for 1 ms. The timing circuit 13 subsequently enables the RF amplifier 3 by sending a keying signal to the keying input. The RF energy from the RF amplifier 3 is filtered by bandpass filter 4 to reduce spurious RF emissions. The filtered signal is passed to a PCB foil micropatch 2 dBi gain antenna 5 which radiates the RF energy to an appropriate receiver. When the timing circuit 13 keys the RF power amplifier 3 it also begins to recirculate the spread spectrum 31 chip code stored in recirculating register 10 at a chip rate of 1 to 1.3 MHz. The chip code in turn causes a voltage swing 0–5 volts at the modulation input of the microprocessor. The voltage swing in conjunction with a modulation setting second resistor R7 creates a proportional current which modulates voltage controlled oscillator 2 thereby generating a spread spectrum FSK signal. This improves the signal to noise ratio at the receiver by reducing required bandwidth and minimizes the chances for intersecting interference. The data is super imposed on the chip code by the resistor 6 as a 1/31 deviation of the total modulation. Two or three adjacent chip code sequences are used to equal one bit time resulting in a baud rate of 14–21 KB/s.
In order for a receiver to demodulate a spread spectrum chip code, it must time lock onto the spread spectrum chip code. Disclosed are three methods of this timing acquisition, one is serial and two are parallel assisted. All methods require some synchronization bits in the transmitted message specifically allocated to code timing acquisition, which allow the receiver to search the code and find a correlation peak. The serial correlator searches one bit time per chip in the code sequence to achieve a plus or minus ½ chip code lock. This search can be hastened by searching one code sequence time instead of one bit time thereby providing a two or three to one speed increase. The parallel correlator searches all 31 chip sequences in parallel so that an initial plus or minus ½ chip synchronization (“lock”) can be achieved in one bit or one chip code sequence time. “Fine” code lock (.+−.¼ chip) br either serial or parallel assisted schemes must be followed by transmitted bit times allocated to allowing the receiver to achieve a higher resolution correlation “time” lock. One-quarter chip lock accuracies perform to within 1.25 dB of optimal code alignment. The receiver's fine code lock algorithm seeks to optimize the correlation peak. Higher levels of code lock can be achieved by searching in smaller fractions of a chip. This can facilitate “time of flight” distance or location measurement applications such that 25 ns, 25 feet, of measurement resolution can be achieved.
The transmitter's microprocessor 8 stores a synchronizing preamble in preamble register 11 of 36 bits for a serial correlator, which are broken into 31 bits for coarse lock 11 and 5 bits for fine lock 12. For the two parallel correlation methods disclosed 6 bits are used in the synchronizing preamble, 1 bit for coarse lock and 5 bits for fine lock. The actual code locking bits are transmitted as alternating ones and zeros so that the receiver's data demodulator can adaptively choose an optimal 1/0 voltage level decision point. The preamble is followed by a single data message synchronization bit 24 then 12 ID address bits 14 and 3 unit type bits 15 from address register 11, then 8 bits of input data from data register 18 and lastly 16 bits of CRC-16 data integrity check 19. The CRC-16 generator 19 is based on the entire proceeding message.
Once the message is transmitted, the timing circuit 13 turns off the enable signal at the enable input to voltage controlled oscillator 2 and the keying input of RF power amplifier 3, regenerates a new random number from random number generator 17, presets that number into the transmit interval wake-up circuit 9 and then sets the microprocessor 8 into the sleep mode. Battery voltage regulation is provided by a micropower regulator 1. Battery voltage is pulse tested to conserve battery life 25.
The CRC-16 generator can have its kernel seeded with an identification number unique to each facility. For example, the kernel can be set by the facility address. Any facility having a transmission system which uses such a unique code as the kernel for the CRC-16 generator can be separated from adjacent facilities without additional transmission time or message bits.
Receiver
The spread spectrum receiver comprises several major blocks:
A. The RF section which converts the received signal to lower frequencies;
B. Chip code generator with means of chip code phase shifting for correlation lock;
C. Means to measure both signal strength and quieting to detect correlation lock over the dynamic range of the system;
D. An adaptive data demodulator tolerant to DC i.e.: long strings of 1's or 0's; and
E. microprocessor algorithms to perform the above.